The present invention relates to rotary screw compressors. In particular, the present invention relates to oil-flooded rotary screw compressors having multiple modules.
Conventional rotary screw air compressors have included multiple modules. These modules are typically arranged in series so that air is compressed in modules until the desired pressure was reached. U.S. Pat. No. 4,076,468 to Persson, incorporated by reference herein, discloses an example of such a compressor. Persson discloses a compressor having two modules positioned in parallel with one another but acting in series. The pressurized air produced in the first module is supplied to the second module. While higher pressures can be achieved by using multiple module compressors, the amount of fluid flow is limited. Because the modules are arranged in series, the compressor can only discharge the amount of fluid that can be moved through a single module.
However, for some equipment using pressurized fluid (e.g. air) the supply of a large amount of air is more important than a supply of highly pressurized air. For example, some types drilling equipment require the continuous supply of air at 100 psi. This equipment typically runs for long periods of time and requires a constant flow of large volumes of air. Other compressed air systems supply pressurized air to equipment by maintaining a large amount of pressurized air in a storage tank. However, due to the continuous operation of the equipment, the demand for air typically exceeds the available supply and the storage tank is quickly depleted, despite the continuous operation of the compressor. Furthermore, while a single module air compressor may generate sufficient discharge pressure to meet the equipment requirements, an undesirably large module would be required to meet the large volume requirements.
Accordingly, there is a need for a compressor that can provide a large volume of pressurized fluid to meet high demand requirements. As disclosed in U.S. Pat. No. 3,597,133, issued to Zeitvogel et al. and incorporated herein by reference, the capacity of single module rotary screw type compressor may be increased by providing a second female screw. The disclosed system includes one male rotor driven by a drive shaft. The rotation of the male rotor and screw causes the simultaneous and parallel rotation of two female rotors. The systems described in the Zeitvogel patent produces a larger volume of compressed air than the traditional compressor system that includes multiple modules arranged in series, but it also has several disadvantages. A system employing only one male rotor to drive multiple female rotors is reliant on the integrity of the one male rotor. Thus, if the male rotor fails, neither female rotor can act to compress the fluid. Moreover, if either female rotor fails, the entire system must be dismantled to disengage the failed female rotor from the male rotor. Such a time-consuming and labor-intensive process drastically reduces the utility and reliability of this type of compressor. In addition, due to the precise tolerances associated with forming a casing having three aligned bores for receiving the intermeshed rotors as well as the need to precisely set the discharge end clearances, such a system is extremely expensive and time consuming to manufacture.
U.S. Pat. No. 5,108,275 to Sager discloses a rotary screw compressor in which one gear acts on two compressor modules. The system includes two compressor modules which have separate inlets, but are arranged to force compressed air through a common output. The system provides some increase in capacity, however, the Sager system also has certain disadvantages. First, the system requires that the inlet ports be located at opposite ends of the compressor casing and drive shaft. This design makes maintaining and servicing the compressor more difficult. Second, the male rotors and the driven female rotors are positioned on the same drive shaft, thereby reducing the axial and radial forces on the shaft to approximately zero. As a result, the loading on the discharge end of the male and female rotors is essentially eliminated. A load on the rotor discharge ends, however, is required to maintain reliability and stability in a compressor module, Sager""s device fails to provide these desirable features. Therefore, there remains a need for a compressor that can produce large quantities of pressurized air and is easy to service and maintain.
The present invention addresses these needs and provides other advantages as well.
A multi-module rotary screw compressor is provided. The compressor includes a compressor casing having an inlet cavity for receiving a fluid to be pressurized. The compressor contains a plurality of rotary screw compressor modules which are positioned to receive air directly from the inlet cavity. Each of the rotary screw compressor modules includes a male rotor intermeshed with a female rotor. A drive shaft is operatively connected to each of the compressor modules through a main gear. Rotation of the drive shaft causes the male rotors to rotate. The rotation of each of the male rotors causes the female rotors to rotate and thereby compress the fluid.
Preferably, the compressor includes a drive gear mounted to the drive shaft. Each of the male rotors includes a driven gear which engages the drive gear so that rotation of the drive shaft and the drive gear causes a corresponding rotation of the driven gears. Preferably, the ratio of the drive gear to each of the driven gears is the same.
The plurality of compressor modules may consist of first and second compressor modules. The first and second compressor modules should be positioned on opposite sides of the drive gear but not 180xc2x0 apart in order to maintain the proper radial loading on the drive shaft. Preferably, the rotors are located approximately 150xc2x0 apart from one another around the drive shaft.
The compressor casing may include an outlet cavity for each of the rotary screw compressor modules whereby compressed fluid produced in each rotary screw compressor module is supplied to the corresponding outlet cavity. Alternatively, the compressor casing may include a common outlet cavity into which the compressed fluid of each of the rotary screw compressor modules is supplied, thereby ensuring that the pressure of the compressed fluid at an outlet of each of the rotary screw compressor modules is substantially the same.
The compressor may be configured so that each of the compressor modules contribute substantially equal volumes of compressed fluid to the outlet cavity. The compressor modules may be oil-flooded rotary screw compressors. The plurality of compressor modules may consist of first and second compressor modules configured so that in the first compressor module the male rotor is positioned above the female rotor and in the second compressor module the male rotor is positioned below said the female rotor.
The compressor may include bearings positioned between the compressor casing and each of the male rotors. These bearings may be positive locking thrust bearings. Each of the driven gears is configured to be disengaged from the drive gear so that the compressor modules may operate independently. If a module is disengaged and the user intends to only use the remaining module, the inlet port corresponding to the disengaged module must be sealed to prevent fluid leakage. Furthermore, an indentical back-up module may be provided to replace a failed module to facilitate the rapid return of the compressor package to twin module operation.
A method of producing compressed air in a compressor casing is also provided. The method includes the steps of: rotating a drive shaft; rotating a first male rotor in a first rotary screw compressor module, wherein the first rotary screw compressor module is operatively connected to the drive shaft; rotating a first female rotor in the first rotary screw compressor module; rotating a second male rotor in a second rotary screw compressor module, wherein the second rotary screw compressor module is operatively connected to the drive shaft; rotating a second female rotor in the second rotary screw compressor module; and providing air to each compressor module through a common inlet cavity so that each compressor module discharges compressed air. The method may include the step positioning the first rotary screw compressor module and the second rotary screw compressor module so that they are on opposite sides of the drive shaft at an angle less than 180xc2x0. In addition, the method may include selecting a degree for the angle (between the first and the second rotary screw compressors) such that sufficient loading is maintained on the drive shaft while minimizing the width of the casing. The method may also additional steps including: providing lubricating fluid to each compressor module; providing bearings between the male rotors and the casing to establish an end clearance for each male rotor. In this latter step, the end clearances may be the same.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.